This invention relates to improvements in the extraction of copper from solutions by reduction with anthraquinols dissolved in a water immiscible solvent.
U.S. Pat. No. 3,820,979 to J. Manassen, entitled Process for the Production of Metals, the disclosure of which is herein incorporated by reference, discloses a process for the production of copper, silver, and mercury from aqueous solutions containing these values. In the process of that patent, a quinolic compound (anthraquinol), which is dissolved in a water immiscible organic solvent, contacts an aqueous solution containing metal values of interest, such as copper ions, in either the cupric or cuprous state, to reduce the metal ions and to produce a metallic powder. After this reduction, the metallic precipitate is separated; the organic and aqueous phases are separated; and, if desired, the quinolic compound, which is oxidized during the process to a quinonic compound (anthraquinone), is regenerated by reduction and used for treating further batches of aqueous metallic salt solutions.
Especially advantageous reducing agents are anthraquinols, which, during the reduction of the metals are oxidized to anthraquinones. Particularly suitable anthraquinols are 2-methyl-anthraquinol, 2-ethyl-anthraquinol, 2-propylanthraquinol, 2-isopropyl anthraquinol, 2-t-butyl anthraquinol, and 2-amyl-anthraquinol. Tetrahydroanthraquinols and 2-substituted tetrahydroanthraquinols can also be used. The oxidized form of these compounds (anthraquinones) can be easily produced by condensation of a suitably substituted diene and naphthaquinone, according to the procedure of Alan et al., Organic Synthesis 22,37 (1947). The quinol can thereafter be made by hydrogenation.
An important consideration in the choice of the particular anthraquinol to be employed is its solubility in the organic solvent system used. Preferred solvent systems suitable for the quinol and for the quinone produced during the process are combinations of nonpolar and polar solvents. It is known that in order to minimize losses due to the evaporation of the organic solvent, nonpolar solvents such as alkyl toluenes, alkyl naphthalenes, or diphenyls are advantageously resorted to. Polar solvents, such as octanol and ethyl hexanol or diisobutylketone are preferred. Esters such as dialkyl phthalates, diaryl phthalates, alkyl benzoates, benzyl acetates, ethyl heptanoates and cyclohexanol acetates or propionates can be used as such or in combination with another organic solvent.
The Manassen patent also teaches that it is possible to reduce and precipitate a large part of the reducible metals contained in the solution by employing an excess of the reducing agent. In addition, it is taught to be advantageous to effect the process in two or more stages, using a suitable quantity of fresh organic solution in each stage.
The Manassen patent, however, does not deal with many of the problems that would be encountered in practicing the process on a commercial scale. Specifically, the patent does not address itself to methods of optimizing the rate of precipitation of the metals of interest nor to conserving the organic extractant employed so as to provide an efficient, continuous process.